It is old and well known to utilize culture media in a container for conducting growth and biochemical reactions wherein the sample of the specimen to be tested is applied to the surface of the medium in the container. Such devices are commonly known as Petri dishes.
Commonly used Petri dishes in the form of a dish having a bottom wall and a peripheral side wall are filled with the molten culture medium and the culture is permitted to solidify or gel. A cover is then loosely applied. In order to prevent surface phenomenon problems such as syneresis, contamination, and condensation of moisture, it has been essential to refrigerate such Petri dishes until they are to be used. Syneresis occurs because of evaporation of the solidified culture medium and the inability of the expelled water vapor to rehydrate the solidified gel. When the temperature differential between the inside of the dish and the environment differ, the effects of this evaporation on the inside cover results in heavy condensation and necessitates that a technician must first dry the interior of the plate before using it. Dehydration occurs more rapidly with warmer temperatures and dry conditions in the environment. Contamination occurs because the cover is loosely applied allowing entrance and exchange of external non-sterile atmospheres.
In an effort to obviate the sterility and dehydration problems, it has been common to provide a plurality of such Petri dishes in a sterile plastic sealed bag. However, it has still been essential to refrigerate the package for certain types of culture media to retard syneresis, contamination and dehydration. Refrigeration has also been necessary for culture media which are subject to oxidation such as those that contain blood, vitamins or antibiotics. Further, refrigeration may be required for extended storage greater than a week. In any event, the shelf life of such culture dishes is very limited, on the order of three or four months. Accordingly, it has been necessary to date the package. As a result, if the package is not used within the time indicated it must be destroyed.
U.S. Pat. No. 4,775,628 proposes to seal a modified Petri dish with a pervious sheet, thereafter apply the molten media through an opening in the bottom wall of the dish, seal the opening and thereafter utilize such a dish in testing by applying the specimen to the pervious sheet. Such an arrangement is not only complex, slow and costly, but necessitates the utilization of a method of using the culture media that has not heretofore been used.
Among the objectives of the present invention are to provide a culture media package which has long shelf life; which minimizes the problems of syneresis, desiccation, and contamination; which provides a smooth surface on the culture medium for receiving the test specimen; which does not require refrigeration; which can be readily shipped; which is not fragile or brittle; which can be provided in various configurations depending upon the type of test needed; which can be utilized in a conventional manner as well known in the art of using Petri dishes; which in some forms provide a Rodac device; which in some forms provide a combined Rodac and conventional culture media package; which is low in cost; which can be produced at high speeds; and which is pleasing in appearance.
In accordance with the invention, the culture media package comprising a container having a bottom wall and a peripheral side wall, a removable insert over the top wall and having a portion defining a planar undersurface bonded to the container and a removable protective cover over said container and insert. The container and insert having radially extending flanges which are bonded to one another. The packages are made by filling the container with molten culture medium in a sterile environment, bonding the insert to the container in a sterile environment, inverting the sealed container such that the molten medium contacts the planar surface of the insert permitting any gases and bubbles to rise toward a space adjacent the bottom of the container and maintaining the container with the insert thereon in an inverted position until the culture medium has solidified. The surface of the culture medium which is to be used for testing takes on the shape of the insert providing the desired test surface when the insert is removed. The removable cover may be applied to the sealed package of the container and insert either before the sealed package is inverted or after the medium has solidified. The package is preferably made from continuous molded plastic strips of connected containers and connected inserts which are filled with medium and sealed, severed from one another, thereafter inverted while the culture medium is still molten and permitted to remain in the inverted position until the culture medium has solidified.